Long pipe relining in Magdeburg

The city of Magdeburg can look back on a truly complex history: It had its beginnings in the years 805 to 965, when the first German emperor of the Holy Roman Empire, Otto the Great, was crowned and declared Magdeburg to be his favourite palace; the gothic cathedral is his last resting place. From what was once an episcopal city, then a Hanseatic city, centre of the reformation and all but destroyed in the Thirty Years’ War, at the beginning of the 18th century Magdeburg was built up to be the strongest fortress in Prussia. After the almost complete destruction in the Second World War, Magdeburg was quickly promoted to the status of a GDR district city and since 1990, with around 240,000 inhabitants, it has been the state capital of Saxony-Anhalt.

The drinking water supply for Magdeburg comes from the idyllic Colbitz-Letzlinger Heide (a heath 30 km to the North of the city). This is not only the largest continuous area of heathland in Central Europe but is also the largest uninhabited region of Germany. Beneath this unspoilt nature there are extensive reserves of groundwater from which the excellent Magdeburg drinking water is taken.

Renovation with a sense of proportion

The planning, construction and operation of the 1,235 km long drinking water network (820 km of water mains and supply distribution pipelines plus 415 km of domestic service pipelines) are down to SWM Städtische Werke Magdeburg GmbH & Co. KG. In addition, SWM operates gas, heat and wastewater sectors for the state capital. Close to half of the drinking water mains and supply pipelines for Magdeburg consist of cast iron pipes which, for the majority, have been in operation for more than a hundred years. The gradual and constant ageing process results in damage scenarios, particularly corrosion and especially in very old sections of pipeline, which necessarily require renewal or renovation. These renovation and/or renewal measures – principally ofthe power, natural the important large water mains – are being carried out by SWM responsibly and successively as and when the financial situation allows.

In the context of these maintenance measures, in the Summer of 2018 SWM started on a roughly 1,000 m long section, renovating the main drinking water pipeline in the Halberstädter Straße between Wiener Straße and Kroatenweg.

An old pipeline in modern surroundings

The key data for this existing pipeline are as follows:

Year of construction:	1897 and in operation ever since
Material:	grey cast iron (GG)
Nominal size:	DN 700
Pressure stage:	PN 10
Condition:	ageing damage as a result of spongiosis and increasing incrustation
Location:	beneath the pavement
Depth:	on average at approx. 2m

 

The Halberstädter Straße is a major and busy arterial road running North-East to South-West with tram rails, two to four traffic lanes, bus traffic, cycle ways and wide pavements which are lined with shops, cafés and restaurants. Also there is an extensive stand of old trees in the immediate area of the drinking water pipeline to be renovated. So it was important to take account of traffic and environmental technology concerns as well as obstructions/incursions for shops and residents and keep these to a minimum. In the context of approval planning there was comprehensive coordination with the Magdeburg city authorities (among others the road closure committee and civil engineering office) as well as the urban green spaces and cemeteries department regarding tree protection concerns. Also numerous on-the-spot discussions with the resident businesses both before and during the construction work by the contracting company meant that the work was able to proceed more or less without problem.

Decision in favour of the tried and tested

The planning done the year before by SWM was agreed with the city of Magdeburg, the existing utility operators and the Magdeburg transport companies among others. As had already been considered and implemented in other completed renovation projects, this provided for a reduction of the pipe diameter from DN 700 to DN 400 as a result of years of declining or static water consumption. After experiences in recent years, when renovation measures were being continuously carried out on old grey cast iron pipelines in the city, once again after cleaning and after camera inspection the existing pipeline did indeed show damage (incrustations, risk of pipe ruptures), but even after 120 years of operation was nevertheless in a passable state of preservation.

It was therefore obvious, considering these underlying conditions, the nature of the area surrounding the worksite and the corresponding economic and ecological considerations, that the renovation should be done mainly using a trenchless technique. In some place however, depending on constraints, the open trench technique would have to be adopted as well, above all to incorporate fire hydrants, branches, connections and sets of valves in the pipeline. In these cases, a reduction in the minimum depth of pipe cover from approx. 2 m to 1.20 m was specified.

So, in the end, SWM opted for the long-pipe relining process (in accordance with DVGW worksheet GW 320-1) for 915 m out of the total of around 1,000 m of DN 700 grey cast iron pipeline using

• DN 400 ductile iron pipes, standard overall length 6 m 
• wall thickness class K 9 
• pressure stage PN 10 
• BLS^® type positive-locking and restrained push-in joints 
• cement mortar lining and 
• a zinc-aluminium coating (400 g/m²) with a finishing layer of blue epoxy resin (EN 545)

The last of these features was decided upon for several reasons: in order to reinforce the galvanic protection effect a 15 % proportion of aluminium is added to the zinc to produce an alloy. In this way, and by increasing the total mass of zinc as compared with the standard zinc coating (200 g/m²), the result is an additional improvement in the technical service life to be expected. Also, the pipes require this coating if the annular space between old and new pipe is filled.

For the renovation of smaller sections, pipes in different materials and dimensions have been used.

Execution: precise, safe and effective

In Spring 2018, after around a year of planning, the renovation project was commenced in two phases in terms of both location and time:

1st phase: Halberstädter Straße from Wiener Straße to Ambrosiusplatz and

2nd phase: Halberstädter Straße from Ambrosiusplatz to Kroatenweg

Construction pits

Because of the route of the existing pipeline, the valves installed and because of changes to the pulling-in sections (it was planned to have pulling-in lengths of up to approx. 300 m), construction pits (for both installation and pulling- through) were excavated in the pavement area of Halberstädter Straße at a distance of 150 to 280 m. The pits were approx. 2.5 m wide, 8.5 m long and, depending on the depth of the existing pipeline, between 2.0 and 2.5 m deep on average. For pulling in the pipes, a Grundoburst 800 G bursting rig from Tracto-Technik GmbH & Co. KG was used which is driven hydraulically and has been developed for the static burst-lining process. Tractive forces of up to 80 tonnes can be achieved with this rig.

Pipe-pulling

The old DN 700 grey cast iron pipeline was first mechanically cleaned and then inspected by camera. The new 6 m long DN 400 pipes in ductile cast iron (GGG) were pulled in by an experienced team from Ludwig Pfeiffer GmbH & Co. KG according to the handling and installation instructions for long-pipe relining using the pulling process. The new pipes were aligned in the construction pit in each case and the BLS^® push-in joints including their protection were assembled with a sheet steel cone sleeve. Using the bursting rig, the pipe string was then pulled 6 m into the old pipeline in each case, draggling on the sheet steel cone.

With reference to the traction forces to be expected for pulling in the pipes, SWM defined the requirements quite clearly. In advance and on the basis of their experience, their specialists estimated the traction forces, with obstacle-free progress, to be at least 6 tonnes (60 kN). With a risk loading of 4 tonnes (40 kN), the planning was based on pullingin forces of approx. 10 tonnes (100 kN). During the work, traction forces of up to 7 tonnes (70 kN) were determined.

The effective speed of pulling-in depends on a number of factors: these include setting up the bursting rig, assembling the rods, assembling and dismantling the traction head, assembly times for installing the pipes and the actual speed of pulling in the pipes. Against this background, it can clearly be seen that the time required for long pulling-in sections is more favourable than for short ones.

In order to get a rough idea of the effective pulling-in speed, a section with a pulling-in length of 200 m can be considered as an example, without the pipe cleaning. For the installation and removal of the bursting rig, the assembly and dismantling of the traction head, installation of the rods and the pulling-in of the pipes, just about 4 days were needed, working between 5 and 12 hours a day.

Finishing work

The annular space remaining between the old pipe and the new pipe was filled with an alkaline insulating material which, according to the requirement set by SWM, had to have a shrinkage/ water separation after curing of less than 1 % by volume and a compressive strength of at least 1.0 N/mm² after 28 days.

The last stage of the work was the pressure testing of the new pipeline using the accelerated normal process according to DVGW worksheet W 400-2 with a test pressure of 15 bar and a test time of one hour as well as the subsequent disinfecting of the pipeline.

Sustainability aspects achieved

The careful planning and preparation of the project, the fine-tuning with respect to adjacent construction projects, diversion concepts, public transport requirements etc. with the city of Magdeburg, the existing utility companies and the Magdeburg transport companies among others as well as the choice of material and installation processes resulted in a successful completion of the renovation project. Numerous aspects of sustainable construction are achieved here. The most important of them are:

economic aspects

• considerable reduction of civil engineering costs by the use of the trenchless relining technique (only intermittent excavations for construction pits, use of the existing route) 
• reduced costs for restoring the pavement surface 
• reduced restriction of traffic (traffic lane, public transport, diversions) 
• minimised impairment of access to the shops 
• fast and secure assembly of the BLS^® push-in joints 
• high rate of installation productivity with the BLS^® push-in joints 
• reduction of the existing pipe diameter (increasing the speed of flow and shortening the dwell time of the drinking water in the pipeline which avoid hygiene problems) 
• a further long working life of more than 100 years

ecological aspects

• only intermittent excavations for construction pits 
• minimising the stoppages of private transport
• short assembly times allowing fast progress of work
• food-grade lining of pipes n high diffusion tightness protects the drinking water
• low servicing and maintenance expense
• no negative impact on the trees

technical aspects

• restrained joints allow for the highest tractive forces and are therefore best suited for long pipe relining 
• pipes and joints allow for operating pressures up to 100 bar according to nominal widthssizes 
• installation does not need special equipment

If, by the end of October 2018, all the documentation, from acceptance protocol to tractive force statements, has been handed over, SWM can tick off the Halberstädter Straße renovation for the next 120 years and get started on the next section.

Keywords

Long pipe relining, renovation, Magdeburg drinking water pipeline, reduction of pipeline cross-section, sustainability

 

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